3.1. Results validation
The roadway with θ = 0° and open outlet is taken as an example to verify the reliability of the numerical simulation results. The shock wave peak overpressure in the unit of different positions is chosen as the study object. Subsequently, the shock wave overpressure and time changing curve are obtained, and the numerical simulation result is compared with the result obtained by Qin (2008), as shown in Fig. 4.
Figure 4 indicates that the numerical simulation result is consistent with the shock wave-overpressure/time-variation trend. Initially, the curve decreases sharply from the maximum, and then changes slowly, and becomes stable. The maximum survey point error is 17 KPa, and the average error is 6 KPa. The two curves are very close, indicating the higher reliability and feasibility of the numerical simulation results presented herein.
3.2. The effect of roadway outlet conditions on distribution of shock wave peak overpressure
In order to study the conditions of the roadway outlet’s effect on the explosion shock waves, the air shock wave overpressures in different positions in the roadways with 0˚ and 90˚ blending angles are selected, to obtain the peak overpressure-distance distribution, as shown in Fig. 5.
As seen in Fig. 5, when θ = 0°, the shock wave peak overpressure is essentially equal in the region of 0–80 m from the explosive source under the condition of roadway outet closure and open. The roadway outlet closure has negligible impact on the shock wave peak overpressure. When the distance to the explosive source is 80–100 m and the roadway outlet is closed, the shock wave peak overpressure suddenly rises, showing an upward trend. In contrast, the shock wave peak overpressure decreases gradually when the roadway outlet is open. When θ = 90°, the peak overpressure distribution has similar features, but differs in different regions, i.e., when the distance to the explosive source is between 0 m and 90 m, the shock wave peak overpressure is essentially equal the same the condition of roadway outlet closure and open. When the distance is between 90 m and 100 m, the shock wave peak overpressure increases under the condition of roadway outlet closure, and reduces with the outlet open.
To further study the effect of the roadway outlet conditions on the explosion shock wave overpressure distribution in different turning roadways and regions, when θ = 0°, the roadway is divided into two zones by an 80 m distance to the explosive source as the boundary; that is, one zone is between 10 m and 70 m, and the other zone is between 80 m and 100 m. When θ = 90°, the roadway is divided into two zones by a 90 m distance to explosive source as the boundary; that is, a 10–80 m zone, and a 90–100 m zone. Subsequently, the corresponding explosion shock wave overpressure and time distribution curves are obtained, under the condition of roadway outlet closure and open, as shown in Figs. 6 and 7.
As seen in Figs. 6(a), 6(b), 7(a), and 7(b), the time changing curves of the shock wave overpressure in different positions are similar to the roadway outlet closure ones. Initially, the peak pressure increases from zero to the maximum, then decreases continuously, increases again to peak, and then begins to reduce. There are two peak values except at the outlet position. One is formed by shock waves passing through different positions after the explosion. The other is formed when the shock waves pass the barriers at the outlet, where only one peak is formed after the stacking of two peaks, and the peak pressure is considerably greater than the second peak pressure in other observation points. Furthermore, the comparison between Figs. 6(a) and 7(a), and 6(b) and 7(b) indicates that the peak pressure when θ = 90˚ decreases and the arrival time to the same distance increases, compared with those when θ = 0˚. Under the condition of outlet closure, two peak overpressures are chosen to obtain their distribution curves in different turning roadways, as seen in Fig. 8.
In the Figs. 8(a) and 8(b), the first peak overpressure overall decreases (excluding at the outlet points) with the increase in the propagation distance, while the second peak overpressure shows opposite characteristics, with the peak overpressure rising gradually as the propagation distance increases, especially at the outlet, where the peak overpressure reaches its maximum. These analyses suggest that, when the outlet is closed, the explosion shock waves have little effect on peak overpressure in the far zone of outlet, due to the shock waves decreasing greatly after the barriers’ reflection away from the outlet. While the explosion shock waves reflection and stacking effects cause peak overpressure increase in the outlet near zone, the maximum peak pressure is formed in the curve. It can be seen that the closed condition of the roadway has a distance effect on the shock wave peak overpressure in the roadway.
Based on Figs. 6(c) and 6(d), 7(c) and 7(d), when the roadway outlet is open, the variation curves of the shock wave overpressure in different positions will increase from zero to peak, and then begin to reduce sharply. In contrast, when the roadway is closed, the pressure curves peak is formed only once. Moreover, the shock wave peak overpressure decreases with the propagation distance increase. Furthermore, the comparison between Figs. 6(c) and 7(c), 6(d) and 7(d) indicates that, as the θ bending angle of the roadway increases, the peak overpressure at the same distance decreases continuously, and the arrival time to the same distance increases. Therefore, the bending angle can change the space-time distribution of the shock wave overpressure in the roadway.
3.3. The influence of roadway outlet conditions on explosive destructive effect partition
Based on the explosion shock wave overpressure’s level of injury to the human body shown in Table 1 (Gu et al., 2009), when the shock wave overpressure is more than 100 KPa in the explosion-affected zone, the zone will be regarded as the dead zone (marked by Zone A). When the shock wave overpressure is between 50 KPa and 100 KPa, the zone will be considered as a serious damage zone (marked by Zone B). When the shock wave overpressure is between 30 KPa and 50 KPa, the zone is identified as a moderate damage zone (marked by Zone C). When the shock wave overpressure is between 20 KPa and 30 KPa, the zone is determined as a slight damage zone (marked by Zone D). When the shock wave overpressure is between 0 KPa and 20 KPa, the zone is determined as a no damage zone (marked by Zone E). Combined with the numerical simulation results, Figs. 9 and 10 show the explosive destruction effect partition in the roadways with 0˚ and 90˚ bending angles, under the condition of roadway outlet closure and open. Table 2 shows each zone range for different curvature turning roadways, based on the explosive destruction effect partition.
Table 1
Explosion shock wave overpressure’ level of injury to human body
Overpressure (KPa) | injury effect |
< 20 | no injuries but be scared |
20 ~ 30 | minor injury |
30 ~ 50 | hearing organ injury or fracture |
50 ~ 100 | severe visceral injury or death |
> 100 | the majority of deaths |
Table 2
Range of explosive destruction effect partition of different curvature turning roadway
roadway type | explosion damage range/m |
zone A | zone B | zone C | zone D | zone E |
θ = 0° | with outlet closure | (0, 8.64) | (8.64, 18.94) | (18.94, 44.7), (93.18, 100) | (44.7, 93.18) | ---- |
with outlet open | (0, 8.44) | (8.44, 18.8) | (18.8, 47.37) | (47.37, 96.24) | (96.24, 100) |
θ = 90° | with outlet closure | (0, 0.5) | (0.5, 2.87) | (2.87, 16.54), (99.46, 100) | (16.54, 65), (95.96, 99.46) | (65, 95.96) |
with outlet open | (0, 0.55) | (0.55, 2.96) | (2.96, 16.44) | (16.44, 65.33) | (65.33, 100) |
In Fig. 9 and Table 2, when the outlet of the roadway with 0˚ bending angle is closed, zones A, B, C, and D are formed in the roadway after the explosion. When the roadway outlet is open, zones A, B, C, D, and E are formed. Comparing between the range of zones when the roadway outlet is closed and open, the ranges of zones A (dead zone) and B (serious damage zone) are essentially the same. When the roadway outlet is closed, the zone C (moderate damage zone) range increases visibly, and causes the zone D (slight damage zone) range to move forward.
In Fig. 10 and Table 2, when the outlet of the roadway with a 90˚ bending angle is closed, zones A, B, C, D, and E are formed in the roadway after explosion. Comparing between the range of zones with the open and closed outlet, the ranges of zones A (dead zone) and zone B (serious damage zone) are essentially equal. However, when the outlet is closed, the zone C (moderate damage zone) and zone D (slight damage zone) ranges increase visibly, and the zone E (no damage zone) range decreases.
Overall, the closure of the roadway outlet increases the damage range of the explosion shock waves and the severity of their impact on the human body. In addition, when the roadway outlet is closed and the bending angle of the roadway is 0˚, the ranges from A to C are clearly larger than the corresponding ranges when the bending angle is 90˚. The zone D (slight damage zone) and zone E (no damage zone) ranges decrease visibly, indicating that the damage range and severity decreases with the increase in the roadway bending angle.